A tungsten‐containing active formylmethanofuran dehydrogenase in the thermophilic archaeon Methanobacterium wolfei

Abstract

Methanobacterium wolfei is a thermophilic methanogenic archaeon which requires tungsten or molybdenum for growth. We have found that the orgainsm contains two formylmethanofuran dehydrogenases, one of which is a tungsten enzymes. Indirect evidence indicated that the other formylmethanofuran dehydrogenase is a molydbenum enzyme. The tungsten enzyme was purified and characterized. The native enzyme had an apparent molecular mass of 130kDa. SDS/PAGE revealed a composition of three subunits of apparent molecular mass 35, 51 and 64kDa, the N terminalamino acid sequences of two of which were determined. 0.3–0.4 mol tungsten/mol enzyme was found but no moybdenum. The pterin cofactor was identified as molybdopterin guanine dincleotide. The purified enzymes exhibited a specific activity of 8.3 μmol · min−1· mg protein−1 and an apparent km for formylmethanofuran and methylviologen of 13μM and 0.4mM, respectively. The optimum temperature for activity was 65°C. At 40–60°C, the rate increased with a Q10 of 1.9; the activation energy of the reaction was 45kJ/mol. The enzyme was found to require potassium ions for thermostability. The oxygen‐sensitive enzyme was not inactivated by cyanide. Copyright © 1992, Wiley Blackwell. All rights reserved